The invention relates, in general, to an implant and, more particularly, an implant for securing a denture to a jaw bone of the type having a base to be inserted into the bone and at least one column for supporting the denture with the base including at least one substantially hollow-cylindrical part which is open at a side remote from the column.
Swiss Pat. No. 604674 discloses a jaw implant comprising a sleeve-like base having a substantially circular cylindrical wall and a front wall closing one end of the sleeve. At this front wall, the base is connected to a column, while on its other end, the base is open. Circumferentially distributed bores are provided in the cylindrical wall and in the transition zone between this wall and the front wall. A rib extends helically on the outer surface of the cylindrical wall.
Swiss Pat. No. 618870 and the corresponding U.S. Pat. No. 4,180,910 disclose jaw implants having a base of two or three sleeve-like, substantially regular cylindrical parts, and a column which is connected by one end to the base and projects to its other end intended for supporting a denture, beyond the hollow-cylindrical base parts. The hollow, circularly-cylindrical base parts are entirely open on their ends remote from the column, but have front walls on their other ends. The cylindrical and front walls of the sleeve-like base parts are provided with bores having a diameter which is substantially smaller than the inside diameter of the sleeve-like base parts.
If an implant in accordance with one of the aforecited three references is inserted in a jaw, considerable forces must be transmitted, for example, during biting. Forces or force components both in the longitudinal direction of the column and transverse thereto may occur. Particularly, the forces acting transversely to the column may produce very high local loads capable of causing and developing resporption of the bone material. This happens, especially, in instances where the implant base comprises a single sleeve-like part or where the forces act on two or three sleeve-like parts of an implant base in a plane passing substantially through the axes of the two, or of all of the base parts.
Implants of the above-mentioned kind are inserted into the jaw so deeply that even the front wall of the hollow-cylindrical base part or parts is embedded in the bone and comes to lie slightly below the initial bone surface. To make such an insertion possible, a hole is milled into the bone for each of the hollow-cylindrical base parts, the hole has a deep portion in the form of an annular gap for receiving the wall of the hollow cylinder, and a shallow, fully cylindrical portion for receiving the front wall thereof. Upon inserting the implant, the bone grows, in, over the front wall or walls again so that eventually only the column projects from the bone.
A rather large amount of bone material must thus be removed in the shallow areas where the holes receive the front walls of the bases. This, of course, is undesirable, especially with an implant to be inserted into the upper jaw. That is, in the upper jaw, the corticalis, that is, the layer of relatively solid bone material, is thin as compared to the corticalis of the lower jaw. Consequently, with holes as described above made in the upper jaw, the implant is held in place by the porous spongiosa alone. That is why it is frequently impossible to obtain a satisfactory anchoring in the upper jaw.